To say that only those three are in the microprocessor 'space' shows a lack of knowledge of what is shipping out in the real world. All the older 8 and 16 bit cores are still shipping in high volume, and the fpga/asic IP cores are also shipping in high volume. And most are NOT based around Arm and Mips. I designed high volume products for over 20 years before using an ARM part and that was based on the cost benefit, not any architectual superiority. Certification only has meaning IF the person can apply the knowledge used to gain his piece of 'paper' in the real world.

Well the good news is engineers are not compelled to take the test.
But if employers and HR people start asking for AAE certification as a pre-condition for certain jobs and work then those that have it will get the work.
But engineers with 20 years experience should be able to schedule a test and pass easily, right?
So then it will be back to a level playing field with the experienced engineers beating out the recent grads that only have the AAE.

I believe that this is a good step by ARM, not because it will generate lot of good programmers but it will certainly proliferate ARM's architecture among the student community and be helpful as a guide for employers in ascertaining a candidates profile. The certification has multiple levels so it's not just about processors but includes software, hardware and systems knowledge which makes for an all round skill for intending to go all the way.
It would probably also help in increasing the arm talent pool in the job market and also aid free lancer embedded programmers who are new to ARM.